Oxidation causes buildup of particulate matter in lubricating oils. This buildup thickens the lubricating oil and causes deposits in engine parts. When the level gets too high, the increase in viscosity results in poor lubrication and an inefficient operation of the engine system. Such inefficiencies result in loss of fuel economy and increased exhaust emissions.
Currently, lubricating oil formulations are rendered resistant to oxidative degradation by the addition to the lubricating oil formulations of free radical scavenger antioxidants such as sterically hindered phenols, hindered amines and mixtures thereof and hydroperoxide decomposers such as zinc dialkyldithiophosphate.
Most of such antioxidants as are presently used are consumed by the oxidation promoters in the oil (the prooxidants) on a stoichiometric basis. Antioxidants can be added to lubricating oil formulations only in limited quantities and consequently even if and when the maximum practical amount is added they are quickly consumed and disappear, with the undefended oil rapidly oxidizing with their disappearance.
Other antioxidants such as copper acetylacetonates, while consuming the prooxidants on a more than stoichiometric basis are still themselves used-up at a rate of less than about 10:1 and therefore, while superior to the phenolic and aminic antioxidants are still not sufficiently long lived or suitable for the next generation of extended drain lube oils or sealed for life/filled for life lubricant environments.
Prooxidants are continuously generated in the lubricant during routine use or added/introduced into the oil by blow-by gases, or exhaust gas recirculation as during the operation of internal combustion engines.
U.S. Pat. No. 4,867,890 teaches oil soluble organo copper compounds as antioxidants. U.S. Pat. No. 5,650,381 teaches a lubricating oil composition which contains from about 100 to 400 ppm of molybdenum from a molybdenum compound which is substantially free of active sulfur and about 750 to 5,000 ppm of a secondary diaryl amine, which provide improved oxidation control and friction modifier performance. U.S. Pat. No. 6,121,211 teaches a lubricating oil composition comprising a base oil of lubricating viscosity and at least one thiocarbamate containing a divalent metal and a sludge preventing and seal protecting amount of at least one aldehyde or epoxide or mixture thereof. JP 53024957 teaches the liquid phase oxidation of cyclohexane into cyclohexanol by oxidizing the cyclohexane with an oxygen containing gas in the liquid phase in the presence of metal salts selected from the group consisting of Cr, V and W of an organic acid or a chelate compound as a catalyst.
U.S. Pat. No. 4,766,228 teaches a metal dihydrocarbyldithiophosphoryl dithiophosphate material containing a metal selected from zinc, cadmium, lead and antimony or an oxygen and/or sulfur-containing molybdenum complex useful as a lubricant additive (see also U.S. Pat. No. 4,882,446). U.S. Pat. No. 5,439,604 teaches compositions containing metal salts of polyalkenyl substituted monounsaturated mono- or dicarboxylic acids which may be used as a compatibilizing material for mixtures of dispersants, detergents, anti-wear and antioxidant materials. U.S. Pat. No. 3,707,498 teaches antioxidant additives comprising a mixture of a metal dialkyldithiocarbamate and a tertiaryalkyl primary amine, where the metal is from Group IIb, IVa and Va.
U.S. Pat. No. 3,351,647 teaches a composition useful as an oil additive that functions as an antioxidant and antiwear agent having the general formula:
wherein R is a substantially hydrocarbon radical; M is a metal selected from the group consisting of zinc, calcium, copper, nickel, cobalt, chromium, lead, and cadmium; A, B and C are radicals selected from the class consisting of hydrogen and substantially hydrocarbon radicals; x is the valence of M; y is from about 0.5 to about 6. U.S. Pat. No. 4,427,560 teaches a formulation containing among other additives an oxidation inhibitor. The oxidation inhibitors comprising sulfur bridge, bis hindered phenols effectively limit or prevent the attack of oxidants on copper/lead metal and preferably comprise bis(dithiobenzyl) metal derivatives having the formula:

U.S. Pat. No. 3,764,534 teaches a composition comprising a lubricating oil and at least one thioorganometallic complex of the formula:
in which M is selected from the transition metals and zinc, cadmium, tin, lead, antimony and bismuth; n is the oxidation degree of M, R1 and R2 are each a monovalent hydrocarbon radical having one to 20 carbon atoms and 0 to 3 heteroatoms selected from the group consisting of halogen, oxygen, sulfur and nitrogen; Y is selected from the hydrogen atom and the radicals R′, R′O, R′S and R′CO in which R′ is a hydrocarbon radical of 1 to 20 carbon atoms; Y and R1 or R2 may form a divalent hydrocarbon radical containing 1 to 20 carbon atoms and 0-3 heteroatoms selected form oxygen, sulfur and nitrogen; and each atom Z is oxygen or sulfur, at least one of the 2n atoms Z being sulfur. It is recited that these materials exhibit high antioxidancy activity even at high temperature. They can be used with base oils of petroleum origin as well as with synthetic base oils. See also GB 1,322,699.
GB 1,358,961 teaches that 9,10-dihydroanthracene acts synergistically with certain metal β-diketone complexes to provide antioxidancy. The metal β-diketone complexes are of the formulaM(-O—CR1═CR2—CR3═O)n wherein M is a metal, n is 2 or 3, R2 is hydrogen or an alkyl group having 1 to 20 carbon atoms and R1 and R3 are alkyl, aryl or alkoxy groups having 1-10 carbons. U.S. Pat. No. 4,849,123 teaches drivetrain fluids comprising oil soluble transition metal compounds which address low temperature thickening of automatic transmission fluids (ATFs) and high temperature thickening or gear oils. When used in combination with zinc dialkyl dithiophosphates, the quantity of metal compound in the ATFs or gear lubricants is important to obtaining the combination of antioxidant and antiwear properties needed for the extended life of the fluids.
U.S. Pat. No. 4,705,641 teaches the combination of copper and molybdenum salts as being an effective antioxidant and antiwear additive for hydrocarbons such as lube oils. The copper salt preferably is selected from the group of carboxylates consisting of oleates, stearates, naphthenates and mixtures thereof and the molybdenum salt preferably is selected from the group of carboxylates consisting of naphthenates, oleates, stearates and mixtures thereof.
U.S. Pat. No. 4,122,033 discloses an oxidation inhibitor and a method for using the oxidation inhibitor for hydrocarbon materials, particularly lube oils. One or more transition metal containing compounds can be utilized in combination with one or more peroxide decomposer compounds selected from aliphatic amines, alkyl selenides, alkyl phosphines and phosphates wherein the aliphatic and alkyl portions of said compound each contain from about 1 to about 50 carbon atoms as oxidation inhibitors in organic compositions subject to auto-oxidation. Among the transition metal compounds useful according to the patent are the salts of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium, molybdenum, tellurium, ruthenium, rhodium, palladium, and silver, to mention a few.
U.S. Pat. No. 5,631,212 teaches an engine oil of improved wear resistance and antioxidancy comprising base oil, an oil soluble copper salt, an oil soluble molybdenum salt, a Group II metal salicylate and a borated polyalkenyl succinimide. Molybdenum salts are the oil soluble salts of synthetic or natural organic acids, preferably C4 to C30 saturated and unsaturated fatty acids, e.g., molynaphthanate, molyhexanate, molyoleate, molyxanthate and molytallate.
U.S. Pat. No. 4,066,561 teaches organometallic complexes of the formula:
wherein, as defined in the patent, n is an integer of from 1 to about 10, preferably from 1 to about 5; A is an aromatic moiety, preferably phenyl or naphthyl; M is a polyvalent metal, such as, for example, Be, Mg, Ca, Ba, Mn, Co, Ni, Pd, Cu, Zn and Cd; X is a radical selected from the group consisting of organophosphoro, organocarboxyl, organoamino, organosulfonyl, organothio, organooxy, nitrate, nitrite, phosphate, sulfate, sulfonate, oxide, hydroxide, carbonate, sulfite, fluoride, chloride, bromide and iodide; R1 and R2 are alkyl of from 1 to about 10 carbon atoms, aryl, hydrogen,
or a combination thereof; R′ is alkyl of from 1 to about 10 carbon atoms, aryl or hydrogen; R3, R4, R5 and R6 are hydrogen, alkyl of from 1 to about 200 carbon atoms, aryl, alkyl-substituted aryl where the alkyl substituent is comprised of form 1 to about 200 carbon amounts, carboxyaryl, carbonylaryl, aminoaryl, mercaptoaryl, halogenoaryl or combinations thereof. The metal complexes reportedly stabilize the lubricant to which they are added against oxidation.
U.S. Pat. No. 5,824,627 teaches a lube oil composition containing a major amount of a lube base oil and a minor amount of an additive having the formula M4-yMOyS4LnQz and mixtures thereof, wherein M is a metal selected from Cr, Mn, Fe, Co, Ni, Cu, and W, L is independently selected organic groups selected from dithiophosphates, thioxanthates, phosphates, dithiocarbamates, thio-phosphates and xanthates, having a sufficient number of carbon atoms to render the additive soluble or dispersible in the oil, and Q is a neutral electron donating compound, y is 1 to 3, n is 2 to 6, and z is zero to 4, and the L provide a total charge sufficient to neutralize the charge on the M4-yMOyS4 core.
U.S. Pat. No. 3,649,660 teaches silylorganometallocenes as being useful antioxidants for organopolysiloxane fluids. The silylorganometallocenes are selected from the class of    (a) polymers having structural units of the formula
    (b) copolymers composed of structural units of the formula
and at least one unit of (a), and    (c) disiloxanes of the formula
where R is a monovalent hydrocarbon radical, R″ is a divalent hydrocarbon radical, and (C5Q4)M(C5Q5) is an organometallocene, where Q is selected from hydrogen, an electron donating organic radical, and an electron withdrawing organic radical and M is a transition metal, a is a whole number equal from 0 to 2 and b is a whole number equal from 0 to 3.
Transition metal is defined to include all metals of Group III to VIII of the Periodic Table capable of forming a π complex with a cyclopentadienyl radical to form a metallocene. The transition metals that are operative in the present invention are, for example, metals having atomic numbers 22 to 28, 40 to 46, and 71 to 78, such as titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zirconium, columbium, molybdenum, technetium, ruthenium, rhodium, palladium, hafnium, tantalum, tungsten, rhenium, osmium, iridium and platinum (see also U.S. Pat. No. 3,745,129).
U.S. Pat. No. 5,015,402 teaches basic metal and multi-metal dihydrocarbyl-phosphorodithioates and phosphoromonothioates as antioxidant additives. These materials are represented by the general formula:[Z]d[RO)2PSS]yMaXb  (I)wherein M and X represent different metal cations selected from the group consisting of zinc, copper, chromium, iron, copper, manganese, calcium, barium, lead, antimony, tin and aluminum; Z is an anion selected from oxygen, hydroxide and carbonate; R is independently a linear or branched alkyl group of 1 to about 200 carbon atoms, or a substituted or unsubstituted aryl group of 6 to about 50 carbon atoms; a and b are integers of at least one and are dependent upon the respective oxidation states of M and X; y is a whole integer which is dependent upon the oxidation states of M and X; and d is an integer of 1 or 2.
As a consequence of more stringent and demanding performance and environmental requirements on lubricating oils, for example fill for life oils, sealed bearings oils and greases, or modern extended drain engine lubricating oils to perform better, for longer periods and under more severe conditions of temperature and load over longer times as manifested by current and future lubricating oil specifications, particularly engine oil classifications for diesel lubricants (PC7 and PC8) and passenger car lubricants (GF-3 and GF-4), more efficient, longer lasting and more robust antioxidants are required for use in the lubricants. Increased performance results in improved fuel economy and reduced exhaust emissions in engine systems, e.g., gasoline engine systems and diesel fuel engine systems, where the diesel fuel has a sulfur content ranging in the amount of about 5-1,000 ppm.